Contents

Social problems

Sassanid society was divided into four classes: priests, warriors, secretaries, and commoners. The latter formed the bulk of the population, served as its sole tax base, and remained its poorest class.

At the climax of Khosrau II's ambitious Byzantine territory conquests in the Levant and much of Asia Minor, taxes rose dramatically, and most people could not pay. Years of Sassanid-Byzantine wars had ruined trade routes and industry, the population's main income sources. Rapid turnover of rulers and increasing provincial landholder power further diminished the Sassanids. Over a period of fourteen years and twelve successive kings, the Sassanid Empire weakened considerably, and the power of the central authority passed into the hands of its generals. Even when a strong king emerged following a series of coups, the Sassanids never completely recovered.

Military

Years of warfare between the Sasanids and the Byzantines, as well as the strain of the Khazar invasion of Transcaucasia, had exhausted the army. No effective ruler followed Khosrau II and this created chaos in society and problems in the provincial administration (until Yazdegerd III came to power). All these factors undermined the strength of the Persian army. Yazdegerd III was merely 8 years old when he came to the throne and lacked experience and didn't try to rebuild the army. The Sasanid Empire was highly decentralized, and was in fact a "confederation" with the Parthians, who themselves retained a high level of independence.[4] However, after the last Sasanid-Byzantine war the Parthians wanted to withdrew from the confederation, and the Sasanians were thus ill-prepared and ill-equipped to mount an effective and cohesive defense against the Muslim armies.[5] Moreover, the powerful northern and eastern Parthian families, the Kust-i Khwarasan and Kust-i Adurbadagan, withdrew to their respective strongholds and made peace with the Arabs, refusing to fight alongside the Sassanids.

Pourshariati argues that the Arab conquest of Mesopotamia "took place, not, as has been conventionally believed, in the years 632–634, after the accession of the last Sasanian king Yazdgerd III (632–651) to power, but in the period from 628 to 632."[6] An important consequence of this change in timeline means that the Arab conquest started precisely when the Sasanians and Parthians were engaged in internecine warfare over who was to succeed the Sasanid throne.[6]

When Arab squadrons made their first raids into Sasanid territory, Yazdegerd III didn't consider them a threat, and he refused to send an army to encounter the invaders. When the main Arab army reached the Persian borders, Yazdegerd III procrastinated in dispatching an army against the Arabs. Even Rostam-e Farokhzad, who was both Eran Spahbod and Viceroy, didn't see the Arabs as a threat. Without opposition, the Arabs had time to consolidate and fortify their positions.

When hostilities between the Sasanids and the Arabs finally began, the Persian army faced fundamental problems. While their heavy cavalry had proved effective against the Roman armies, it was too slow and regimented to act with full force against the agile and unpredictable lightly armed Arab cavalry and foot archers.

The Persian army had a few initial successes. War elephants temporarily stopped the Arab army, but when Arab veterans returned from the Syrian fronts where they had been fighting against Byzantine armies, they taught the Arab army how to deal with these beasts. Thus war elephants had lost their effectiveness on the battlefield.

These factors contributed to the decisive Sasanid defeat at the Battle of al-Qādisiyyah. The Persians, who had only one generation before conquered Egypt and Asia Minor, lost decisive battles when nimble, lightly armed Arabs accustomed to skirmishes and desert warfare attacked them. The Arab squadrons defeated the Persian army in several more battles culminating in the Battle of Nahāvand, the last major battle of the Sasanids. The Sasanid dynasty came to an end with the death of Yazdegerd III in 651.